(1) Field of the Invention
The present invention relates to a flour milling method and a flour milling system having steps of such as breaking, grading, purification and reduction for the flour milling of wheat grains, and more particularly to a flour milling method having a sorting step for raw wheat grains and a flour milling system adopting the method.
(2) Description of the Related Art
As in a cross-sectional view of an inside structure of a wheat grain, there is a plurality of layers called layers of pericarp, testa and aleuron sequentially positioned from a surface portion of the wheat grains, and there is starch and gluten-parenchyma further inside thereof. It is well known that ash contents are largely contained especially in the layers of pericarp, testa and aleuron within the above constituents. In this specification, the layers of pericarp, testa and aleuron are generally called an epidermis. The wheat grain also has a peculiar longitudinal groove called a crease portion which goes deep into the inside thereof.
FIG. 1 shows a flour milling flow 100 based on a conventional flour milling system which is for producing high quality product wheat flour and in which, after the raw wheat grains are polished, the polished wheat grains are milled through a plurality of breaking steps, and the wheat grains thus milled are sifted out or classified. After foreign matters such as small stones and metal pieces or fragments are removed at a cleaning unit 108, the raw wheat grains are introduced into a polishing unit 101. The raw wheat grains are polished at the polishing unit 101 and are forwarded to a first break 102 via a transporting passage 109. Wheat particles milled by the opposing rolls 102a and 102b of the first break 102 into particles of various sizes are sifted out by a sifter 103 into respective particle sizes. The wheat flour in a small particle size (e.g., smaller than 125 .mu.m) becomes product flour, and the wheat flour in large particle size (e.g., larger than 850 .mu.m) is forwarded to a second break 104. Generally, the wheat flour in an intermediate particle size is supplied to steps called such as smoothing (not shown), purification (not shown) and reduction (not shown).
The wheat flour forwarded from the first break 102 and introduced into the second break 104 at a downstream of the first break is milled by breaking, and the flour thus milled is sifted out by a sifter 105 into product flour whose particle size is small, wheat flour whose particle size is large, and semolina whose particle size is intermediate. Then, these kinds of flour thus sifted out are forwarded to respectively suited steps to follow. That is, at a third break 106 at a further downstream as shown in FIG. 1, the flour milled is sifted out by a sifter 107 and then is forwarded to appropriate steps according to particle sizes. The later the breaking step is, the larger the epidermis contents become in the raw materials introduced.
In the above described conventional flour milling system, irrespective of whether or not a wheat polisher is used, the sifting by employing such system as a sifter is used after the milling in order to produce high quality flour with a high yield. The quality of flour depends on how the wheat flour with little epidermis can be sifted out, and how a large volume flour with ash contents lower than the related standards can be produced.
That is, in order to produce quality flour with a high yield according to a conventional technique, it was necessary to establish a highly precise and highly efficient sifting technique. However, there is a limit in the technique in enhancing the purity of the wheat flour by the operation of sifting and purification means.
Even if a technique with which the epidermis at wheat surfaces is removed in advance by a wheat polisher is introduced, practically it is difficult at the present stage to produce wheat flour of a better quality by the operation of sifting and purification means.